My present invention relates to a platen press and, more particularly, to a multiplaten press for the production of boards from wood materials.
Platen presses and especially multiplaten presses are used for the pressing of mats of materials containing wood inch boards. Such materials can include wood fibers and wood particles or sawdust, with or without binders, usually synthetic resin binders, which may or may not be heat-activatable and where the platens are usually arrayed one above the other to form press gaps.
The platen press systems with which the invention is primarily concerned are those which provide the press with a suction unit for drawing off by suction gases produced during the pressing of the boards. The press platens in this case are heated platens and the boards which are produced are particle board, OSB (oriented strand board) or MDS (medium densified fiber) board.
The mats of the wood material to be pressed are usually fed to the press gaps between the platens on charging plates or trays, charging screens or sieves or like supports or are supplied to the press by belt feeders. The press can then be closed and the mats pressed to boards within the press gap. During the hot pressing process, steam and gases can be evolved which, without the suction unit, would be released into the atmosphere and might be an environmental contaminant. In the processes with which the invention is concerned, the evolved gasses and steam are drawn off by the suction unit and can be trapped in a gas cleaner without being released into the atmosphere. Those gases may include gases evolved by any binder which may be combined with the wood chips, particles or fibers as well as those evolved by the wood materials themselves.
The platen press is usually preceded by a charging device for supplying the mats to the platens and by an emptying or charging device which removes the boards from the press. Units for drawing off the fumes by suction have, in the past, included relatively large hoods or enclosures which generally encompass at least the press and the press-emptying apparatus. As a consequence large screen blowers were required to handle the comparatively large volumes of gas (evolved vapors and ambient air) which were required. For example, the suction unit frequently was required to draw off not only the evolved fibers but also cooling air which had to be supplied to the press.
The drawn off gases required processing, for example with after-burners or the like to destroy the drawn-off vapors. Frequently the proportion of combustibles in the drawn off gas was insufficient to permit effective destruction of the vapors and it was necessary to add fuel to the system to ensure destruction of the evolved vapors. The operation was, therefore, expensive and the equipment evolved had to be sizable.
Multiplaten presses have been provided heretofore with spacers or spacer frames between the platens and wherein heat-resistant seals could be provided between the platens. The platens were provided with gaps running in the longitudinal direction of the platens and which were connected by transverse passages so that the press gaps themselves were interconnected. In such a system the evolved gas could be collected by a pipe system in a tank. The pipe system could use flexible lengths of pipe which could be provided on opposite sides of the platen as, for example, in U.S. Pat. No. 4,409,170. The systems described in this patent are also expensive and in many cases there is insufficient room alongside the press platen to provide the duct work such systems require.
It is, therefore, the principal object of the present invention to provide an improved platen press, especially a multiplaten press, which is not only of simpler construction than those provided heretofore and can be operated reliably and economically to evacuate evolved gases and steam, but which is also of simpler construction and space-saving design.
More specifically, it is an object of the present invention to provide a platen press with improved and evacuation of vapor from the press gap. Another object of this invention is to provide a platen press which obviates drawbacks of earlier systems.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a platen press for the pressing of mats of wood material into pressed board which comprises:
a plurality of platens disposed one above another between upper and lower press sides and defining press gaps between then for receiving wood-containing mats and pressing the mats to form boards;
seals between the platens around the gaps for sealing the gaps upon closing of the press;
passages formed in the platens and communicating with one another and with the gaps inwardly of the seals for forming at least one evacuating duct; and
at least one suction conduit on one of the sides of the press and communicating with the duct at least in a closed position of the press for evacuating gases evolved from the mats during pressing thereof.
According to the invention, therefore, a plurality of platens arranged one above another in the multiplaten press define press gaps between them, each of which is adapted to receive a mat of wooden material so that when the press is closed and the material is compressed between the heated platen, vapors are evolved which are drawn off by a suction unit.
According to the invention, seals are arranged around the periphery of the press platens around the press gaps and seal these gaps upon closure of the press. Each of the press platens can have one or more passages which, upon closure of the press, form evacuation ducts communicating with the press gaps and the upper side of the press and/or the lower side of the press for one or more conduits which communicate with the evacuation ducts.
As a consequence, a direct evacuation of the released vapors is possible since the press gaps themselves are peripherally sealed and the suction conduit on one of the upper or lower sides of the press can directly evacuate the communicating press gaps through passages formed in the platens.
As a consequence it is no longer necessary to evacuate ambient or cooling air with the evolved vapors and in large volumes. Rather the evolved vapors can be sucked off and efficiently burned so that the platen press according to the invention can operate completely in an environmentally sound manner.
Because the external duct work along the sides of the platens is not required, the construction of the press is simplified and the press can take up less space.
The conduits, according to the invention, communicate with the passages at the ends of the platens and press via communicating passages formed in the platens within the seals. The conduits in the upper and/or lower sides of the press ensure that the press will be laterally free from conduits and either rigid or flexible duct work and thus achieve an economy of construction and space which has not been possible heretofore. The conduits, usually a bundle of conduits connected together and to a common suction blower, can be provided at each end of the press in one or the other of the fixed press plates, e.g. the upper press plates so that there is no relative movement between the conduits or between the conduit and the upper and lower press plates or beds.
The passages formed in the platens can be vertical and aligned so that they form continuous evacuating ducts running the full height of the stack of platens. These passages can be flush with one another.
The invention is applicable not only to multiplaten presses but also to single platen presses having an upper and lower press plate or bed. Only a passage in one or the other of these beds is then required to communicate with the evacuating duct formed by a passage at an end of the platen within the seal and communicating with the press gap.
While it is preferred to provide the conduit exclusively in the upper press platen, it has been found to be advantageous to provide conduits in both the upper and lower press plate for connection to respective suction blowers.
Advantageously, an array of passages are formed in equispaced relationship at each end of the press and in the press platen for communication with corresponding numbers of conduits. In that case, in the middle of the press or along the longitudinal edges of the platens between those arrays of passages, there are neither passages nor evacuation conduits. In this case, the dimensions, at least in their widths of the platens by comparison with the platens of prior art presses, need not be increased. The provision of multiple evacuation conduits and passages at each end also affords the advantage that steam can be drawn off in large quantities. This is especially desirable for the production of OSB boards since there the steam predominantly emerges from the mats at the board ends. Only toward the end of a press operation is there an increase in lateral steam evolution.
It has been found to be advantageous to provide the evacuating ducts so that they are equidistantly spaced across the width of the press platens so that a uniform evacuation of the vapors and gases which are released can be ensured. The evacuating ducts can be formed by boards in the platens which are aligned and flush with one another, the boards forming the aforementioned passages.
The suction conduits, in turn, are aligned with and flush with the passages on the lower side of the upper press bed or uppermost press plate or on the underside of the lower press plate or press bed. There the suction conduits communicate with the passages on the upper side of the uppermost platen or the lower side of the lowermost platen, respectively.
To the extent that a multiplicity of suction conduits are provided on each end of the press, they may be joined in suction conduit bundles, each of which communicate with one or more blower devices. When there is a single suction conduit bundle at each end, each bundle may communicate with a respective intake side of a blower.
According to a further feature of the invention in the suction conduit and/or the suction passages, valve elements, for example, flat valves, may be provided. The evolved gases may remain in the suction passages while these valves are closed during an initial press stage and only upon opening of the valve during a subsequent press stage are drawn off by suction. This permits a higher valve pressure to be maintained at least during the initial press stages which has been found to be advantageous for the pressing process and the property of the boards produced. The valve flaps can be opened during the concluding stages of pressing.
It has been found to be advantageous moreover to provide the apparatus with a steam generator unit for feeding steam into the press gaps during, before and/after the pressing process. The term xe2x80x9csteamxe2x80x9d means water vapor and preferably saturated steam. Basically, however, other gaseous fluid media can be fed into the system. For this purpose, steam supply conduits are provided which can communicate with the suction conduits and thus directly or indirectly with the passages formed by the aligned boards in platens. The steam is thus distributed to the press gap via the vapor evacuation system. The steam can positively influence the pressing process by, for example, reducing the press time and can be an important advantage with respect to board quality since it can prevent excess moisture loss at the edges of the boards and assist in rendering the board temperature more uniform during press operation. The result is a significant increase in press board quality.
The suction ducts thus have a dual function and the suction conduits can be provided with valve members such as flaps to enable the steam supply ducts to be shut off or connected to the press gaps. It is, however, also possible to provide separate steam supply ducts which can communicate with passages in the platen and on the upper press bed or lower press bed and which can communicate with the press platens through separate boards in the uppermost and lowermost platens.
Especially advantageous is an embodiment in which the steam supply ducts and the suction conduits communicate with one another and each has a valve flap for blocking flow therethrough so that in one position of the valve, flow of steam to the gaps is provided and in another, the gaps can be evacuated.
The press gaps when charged with steam must permit the steam to be distributed uniformly in the gap so as to ensure a uniform temperature distribution. The supply-saturated steam forms a steam lock which allows heating to temperatures of up to 160xc2x0 C. and usually about 140xc2x0 C. so that excessive temperature losses at the edges of the board will not occur. To prevent stressing or damaging the seals, the valve members can be provided as safety valves or pressure relief valves which can prevent excessive pressure buildup although it is also possible to provide in parallel with each of the aforementioned valves a pressure-limiting or pressure-relief valve.
The press of the invention is usually used in the production of boards of wood material of a thickness of about 6 mm to about 41 mm. The seals thus should be capable of compensating for this variation in the pressing gap width. This can be achieved according to the invention by providing the seals as an inflatable or expandable bladder and expanding the seals with a gas, for example, compressed air. The seals are then hollow and expandable. Depending upon the board thickness, the seals can be inflated or expanded to a predetermined degree with compressed air so that the sealing action is ensured regardless of the board thickness.
According to the invention, the seals can have base bodies enabling their attachment to the respective press platen and to which the expandable sealing body is connected. The sealing body can be of circular cross section, oval cross section or polygonal cross section. The seal itself is preferably composed of a heat-resistant material, especially a synthetic resin, like silicone or a fluoroelastomer which can withstand temperatures of 220xc2x0 C. to 250xc2x0 C. which can be reached in the press.
To facilitate attachment of the seal to the platen, it has been found to be advantageous to provide the platen with a mounting recess in which the base body is received and can be affixed by screws, rivets or by an adhesive.
The seal preferably engages the platen through the intermediary of one or more thermal insulating elements, for example, insulating bodies or layers, especially strip-shaped insulators. Such insulation prevents excessive heating of the seal by the heated platen and allows high temperature to be produced in the press without problems or endangering of the seal. The insulating elements can be composed, for example, of a silicone or a ceramic.
The seals can be provided directly or indirectly on the press platens or heating platens whereby they can engage the neighboring platens directly or indirectly or also can bear upon charging plates or charging sieves or screens on which the mats are fed into the press, especially when a structure is to be formed on the plate and is to be transferred from the charging plate to the board. The edge portions of these charging plates or screws can be provided with an insulating strip which are designed to protect the seals and thereby increase the seal life and the sealing effect. The edge covering of such screens or plates may be composed of silicone or may be silicone impregnated layers.
In embodiments in which the seals, upon closure of the press, do not rest against a charging plate or charging screen with corresponding edge coverings, it is advantageous for the seals to be juxtaposed with press platen surfaces whose edge regions are provided with insulating elements in the form of insulating strips or layers against which the seal can bear. Such an embodiment in which the insulating element is received in a mounting recess in the press platen and is composed of a heat-resistant synthetic resin such as a silicon or ceramic can improve the press efficiency. The heat-resistant or insulating element can be held in place by screws, rivets or adhesive bonding. In a preferred embodiment, however, the insulating element is held in place by means of one or more clamps which can be C-shaped, U-shaped or L-shaped and can secure the attached member in a recess, if desired.
The insulating elements or strips can be of trapezoidal cross section and received in a trapezoidal section or partially trapezoidal mounting press. Finally, the evacuation conduit and/or the steam supply conduit can be formed as insulated ducts with an insulating jacket or an insulating layer to avoid thermal losses. The ducts and conduits can also be externally heated.